Light field 3D display technology is the rise of popular naked eye 3D display technology in recent years, which is based on the basic principle of four-dimensional light field reproduction. The four-dimensional light field refers to the information in the space that includes the direction information in addition to the three-dimensional coordinate information of the space of the exit point. Therefore, ray information with direction must be recorded to completely restore the 3D scene. Usually, a ray of light is uniquely represented by recording the coordinates of the intersection of the space light and the two planes parallel to each other. As shown in FIGS. 1, A and B are two planes parallel to each other in space, and light C is respectively intersected with two planes at A0(xa, ya) and B0(xb, yb). Through the intersection points on the two planes, the light direction information can be obtained, that is A0B0(xb−xa, yb−ya), only need to re-trace the light to re-focus, restore the recorded three-dimensional scene, to achieve true three-dimensional display. At present, the microlens arrays are mainly used to record and restore the information of the light field so as to realize the three-dimensional display of the light field.
However, due to the convergence of light by the microlenses, light passes through the microlenses and forms a clear image only near the focal point. Leaving the focus, the sharpness of the image decreases rapidly, and the farther the out of focus position is, the worse the image clarity is, which greatly limits the depth of field of the 3D display. At present, in order to solve this problem, a multi-focal optical system design has been proposed so that the light can be focused at different positions to improve the depth of field of the display system. However, the existing multi-focus system structure is more complex, not suitable for system integration.